为了更好地将植物转换成生物燃料，美国能源部劳伦斯利弗莫尔实验室、劳伦斯伯克利国家实验室以及国家可再生能源实验室的研究人员合作，采用不同的显微方法，深入到百日草叶片细胞的深处，在纳米尺度研究出这种最常见花园植物的化学成分和植物细胞壁结构。该研究发表在近期出版的《植物生理学》杂志。
百日草是一种常见的一年生草本植物，茎直立粗壮，上被短毛，表面粗糙。叶形为卵圆形至长椭圆形，叶全缘，上被短刚毛。头状花序单生枝端，梗甚长。其幼苗的叶片为深绿色，含有大量的叶绿体和丰富的单细胞，可在培养液中生长数天。在培养过程中，其细胞形状会发生改变，形成管状细胞，负责将水和矿物质从根部运输到叶片。其木质部含大量纤维素和木质素，是近年来生物燃料的研究重点。
纤维素是一种多糖，在酶的作用下，可分解为醇类及其他化学成分，可替代燃料。要想使相关反应有效率，需要在多个空间尺度上了解反应发生的进程。而要想获取糖，还必须想方设法克服由细胞壁木质素纤维素结晶所提供的疏水保护。植物有两种重要的聚合物，统称为木质纤维素，难于溶解，耐化学试剂和机械破损，是植物的结构组织。细胞壁的木质素极难被打破，因此科学家需要对细胞壁组织有着透彻的了解，才能确定最佳的方法来打破它们。
过去人们对植物细胞壁详细的三维分子结构知之甚少。此次，研究人员利用原子力显微镜、荧光显微镜及以傅氏转换红外线光谱分析仪等不同的显微方法，得以详细研究百日草的细胞、细胞亚结构以及细胞壁组织的精细结构，甚至可以对单细胞进行化学成分分析。这对评估植物的各种化学反应和酶处理具有十分重要的意义。
科学家表示，拥有在纳米尺度观察植物细胞表面的能力，并结合化学成分分析，可以大大提高人们对细胞壁分子结构的理解。同时，高分辨率的结构模型，对于将生物质转化为液体燃料至关重要，可以加快人类利用木质纤维素生产生物燃料的进程。(生物谷Bioon.com)
生物谷推荐原文出处：
Plant Physiology doi：10.1104/pp.110.155242
Imaging Cell Wall Architecture in Single Zinnia elegans Tracheary Elements
Catherine I. Lacayo1, Alexander J. Malkin1, Hoi-Ying N. Holman2, Liang Chen2, Shi-You Ding3, Mona S. Hwang1 and Michael P. Thelen1,4
1 Lawrence Livermore National Laboratory; 2 Lawrence Berkeley National Laboratory; 3 National Renewable Energy Laboratory
The chemical and structural organization of the plant cell wall was examined in Zinnia elegans tracheary elements (TEs), which specialize by developing prominent secondary wall thickenings underlying the primary wall during xylogenesis in vitro. Three imaging platforms were used in conjunction with chemical extraction of wall components to investigate the composition and structure of single Zinnia TEs. Using fluorescence microscopy with a GFP-tagged Clostridium thermocellum family 3 carbohydrate-binding module specific for crystalline cellulose, we found that cellulose accessibility and binding in TEs increased significantly following an acidified chlorite treatment. Examination of chemical composition by synchrotron radiation-based Fourier-transform infrared spectromicroscopy indicated a loss of lignin and a modest loss of other polysaccharides in treated TEs. Atomic force microscopy (AFM) was used to extensively characterize the topography of cell wall surfaces in TEs, revealing an outer granular matrix covering the underlying meshwork of cellulose fibrils. The internal organization of TEs was determined using secondary wall fragments generated by sonication. AFM revealed that the resulting rings, spirals and reticulate structures were composed of fibrils arranged in parallel. Based on these combined results, we generated an architectural model of Zinnia TEs comprised of three layers: an outermost granular layer, a middle primary wall composed of a meshwork of cellulose fibrils, and inner secondary wall thickenings containing parallel cellulose fibrils. In addition to insights in plant biology, studies using Zinnia TEs could prove especially productive in assessing cell wall responses to enzymatic and microbial degradation, thus aiding current efforts in lignocellulosic biofuel production.
